Rolling bearings are mounted in power transmission mechanisms of motor vehicles, construction machines, etc, such as transmissions, differentials and speed reducers, as well as in travel units thereof, which include the above-mentioned power transmission mechanisms.
Rolling bearings used in some of these travel units are lubricated by the same oil used to lubricate the entire power transmission mechanism.
Oil stored in the cases of power transmission mechanisms such as transmissions, differentials and speed reducers contains foreign matter such as wear dust (including iron dust) originating from gears in relatively large amounts. Foreign matter that enters the interior of a rolling bearing could get wedged between moving parts of the bearing, causing flaking of raceways and rolling surfaces, which in turn reduces the durability of the rolling bearing.
In order to prevent entry of foreign matter, a rolling bearing is proposed including a filter attached to a seal ring mounted to the rolling bearing. This seal ring carries filters which cover oil flow passages formed in the seal ring and adapted to capture foreign matter contained in oil (see e.g. JP Patent Publication 6-323335A and JP Patent Publication 2002-250354A).
Travel units of some of motor vehicles, construction machines, etc. include, in addition to power transmission mechanisms such as a transmission and a speed reducer, oil-lubricated rolling bearings.
Such travel units include a travel unit 4 used in a dump truck 1 used in mines (construction machine), as shown in FIG. 16. This dump truck 1 includes a chassis 2 supporting a load deck and a driver's cab, and supported by a plurality of drive wheels (tires) 3. The dump truck further includes travel units 4 for driving the respective drive wheels 3.
As shown in FIG. 15, each travel unit 4 includes a driving source or a travel motor 5, and a shaft 6 connected to the rotary shaft of the motor 5. A power transmission mechanism T or a speed reducer is mounted around the distal end portion of the shaft 6.
A stationary axle or a spindle 7 is provided around the shaft 6. The body 9 of each drive wheel 3 is mounted around the spindle 7 through rolling bearings 10. The rotation of the wheel body 9 is transmitted to the tire of the drive wheel 3 through a rim 8.
The speed reducer can be any of many known types according to how the motor vehicle or construction machine is used. The speed reducer of the travel unit 4 shown in FIG. 15 is a planetary gear mechanism 50 including a first planetary gear unit 50a and a second planetary gear unit 50b. The rotation of the shaft 6 is reduced by the two planetary gear units 50a and 50b and transmitted to the wheel body 9.
The first planetary gear unit 50a includes a first sun gear 51 which rotates together with the shaft 6, a plurality of first planetary gears 52 meshing with the first sun gear 51, and an outer ring gear 53 meshing with the first planetary gears 52. A coupling member 53a rotatable about the shaft 6 is connected to the outer ring gear 53.
The second planetary gear unit 50b includes a second sun gear 54 which rotates about the shaft 6 together with the coupling member 53a, and second planetary gears 55 meshing with the second sun gear 54. The second planetary gears 55 are rotatable about respective support shafts 56b of a planetary carrier 56 and mesh with an outer ring gear 59a which rotates together with the wheel body 9. The planetary carrier 56 has an extension 56a fixedly splined to an inner peripheral portion 7a of the spindle 7. A bearing presser member (retainer) 17 is disposed between the end surfaces of the planetary carrier 56 and the spindle 7, keeping the end surfaces spaced apart from each other.
When the shaft 6 is rotated about its axis by the travel motor 5, the first sun gear 51 is rotated about its axis by the shaft 6. The first planetary gears 52 are thus rotated by the first sun gear 51 within the outer ring gear 53. When the first planetary gears 52 are rotated, the coupling member 53a is rotated together with first planetary gears 52, so that the second sun gear 54, which meshes with the coupling member 53a, rotates about its axis.
When the second sun gear 54 rotates, the second planetary gears 55 rotate about the respective support shafts 56b of the planetary carrier 56, thus rotating the wheel body 9 through the outer ring gear 59a, which meshes with the second planetary gears 55. The rotation of the wheel body 9 is transmitted to the drive wheel 3 through the rim 8, moving the dump truck 1, used in mines (see e.g. JP Patent Publication 2009-204016A and US Patent Publication 2004/0065169).
The roller bearings 10 used in this travel unit 4 between the spindle 7 and the wheel body 9 are two single row tapered roller bearings. Tapered roller bearings are frequently used as the rolling bearings 10 because rolling bearings used in construction machines have to withstand large radial loads.
A tapered roller bearing includes tapered rollers as rolling elements 13, and inner and outer races 12 and 11 having raceways 12a and 11a and arranged such that the distance between the raceways 11a and 12a gradually decreases in one axial direction. (In the case of each of the bearings 10 of FIG. 15, this direction is the direction toward the other bearing 10.) The inner race 12 of each of the bearings 10 is pressed in the above one axial direction relative to the outer race 11, thereby applying a preload to the respective rolling elements 13. In particular, the preload is applied by pressing the bearing presser member 17 against the spindle 7 by tightening bolts 17a, thereby applying axial compressive force to the inner races 12 of the respective bearings 10 by the bearing presser member 17 and another opposite bearing presser member 18, respectively.
The travel unit 4 may include a rotation sensor or sensors provided on one axial side of the rolling bearings 10 for detecting e.g. the rotational direction, rotational speed, rotational angle, rotational acceleration, etc. so as to use the output signals from the sensor or sensors to control rotation of the rotary shaft of e.g. the motor.